The present invention is directed to a combination breather-drain suitable for use with explosion proof electrical housings and conduits.
An example of a condensation drain for explosion proof fittings is shown in the U.S. Patent to Hardage No. 2,297,830. This condensation drain is adapted to be arranged in the bottom wall of an enclosed explosion proof switch housing and is comprised of a body formed with a passage extending therethrough and adapted to communicate with the interior of the housing. The passage is formed with axially spaced apart portions threaded internally in step pitch. A stem formed with axially spaced apart portions having external threads thereon in step pitch complimentary to the threaded portions of the passage is threaded into the body. The portion of the stem intermediate the threaded portions is of reduced cross-section and the threaded portions of the stem are so spaced that when one threaded portion of the stem is moved out of engagement with the complimentary threaded portion of the passage, the other threaded portion of the stem is in threaded engagement with the other threaded portion of the passage. The stem is provided with stop means cooperable with the body to prevent disengagement of both threaded portions simultaneously. With this construction, there is constant drainage between the threads of the innermost threaded portion and since the lower threaded portions are out of engagement, the condensate can be readily drained. Over a long period of time, the passage between the innermost threaded portions may become filled up or plugged with foreign matter, in which event it is necessary to screw the stem inwardly threading the innermost portion of the stem out of engagement with its complimentary threaded portion and in so doing cleaning the thread connections. During this operation, the outermost threaded portion 21 of the stem will be threaded into the lower end of the body and thus a flame tight joint will be established at the lower end of the body previous to the time the flame tight joint at the upper end of the body is broken. Since the condensation drain is located in the bottom of the explosion proof fitting, there is no provision made for the introduction of ventilating air into the interior of the fitting.
It is also known in the art to provide a universal fitting for explosion proof housings which can act either as a breather or a condensation drain depending upon its location in the explosion proof housing. The universal fitting may be comprised of a plug-type device having a threaded clearance sufficiently small to be explosion proof, but open enough to allow air or water to pass. When this device is located in the bottom of an explosion proof housing, it will act as a drain and when mounted in the top of the housing, it will act as a breather or air vent. The universal fitting may also consist of a series of metal baffles assembled in series instead of a threaded passage. The baffles are so arranged as to render the construction explosion proof while providing a lower resistance to the passage of air and water. Once again, this type of universal fitting can be mounted either in the bottom of the explosion proof housing or the top depending upon its desired function.
In many instances, it is undesirable to use such a universal fitting as a breather on the top of an explosion-proof housing that is exposed to driving rain or hose-down operations because of the possibility of the entry of water through the top breather. However, when only a bottom drain is used without a breather on top, the free drainage of condensed water from the enclosure may not occur.